FIG. 9 is a sectional view of optical sensor 900 that can be used typically for detecting viruses (e.g., PTL1). Optical sensor 900 includes first metal layer 902 and second metal layer 903. A bottom face of first metal layer 902 faces a top face of second metal layer 903. First metal layer 902 is fixed to supporting part 905, and second metal layer 903 is fixed to supporting part 906 to retain their shapes. The thickness of first metal layer 902 is in a range from 30 nm to 45 nm. The thickness of second metal layer 903 is 100 nm or more.
Hollow area 904 is provided between first metal layer 902 and second metal layer 903. Hollow area 904 is configured to be filled with sample 908 including solvent 908A, non-specific specimen 908B, and a substance to be detected (i.e. analyte) 908C. Acceptors 907 are physically adsorbed on at least one of the bottom face of first metal layer 902 and the top face of second metal layer 903.
A light supplied from light source 909, which is a type of electromagnetic source, to first metal layer 902 can be optically resonated between first boundary face 902B of first metal layer 902 and hollow area 904 and second boundary face 903A of second metal layer 903 and hollow area 904. If analyte 908C that establishes specific binding with acceptor 907 is present in sample 908, specific binding of acceptor 907 and analyte 908C is established, and thus a dielectric constant on first boundary face 902B and/or a dielectric constant on second boundary face 903A change. As a result, the optical resonance condition changes, and resonance absorption wavelength against light 909A supplied from light source 909 also changes. Detector 910 can detect this change as color change 909B. Visual detection can be used as one of detecting methods.
Optical sensor 900 does not need a prism. In addition, light 909A supplied from light source 909 does not need to have a certain polarization state or coherence. As a result, small and simple optical sensor 900 can be configured.